1. Field of the Invention
The invention relates to a method for controlling lots dispatch of tool groups, and more particularly, to a method for balancing tool loading whenever the productions increase or decrease.
2. Description of the Prior Art
Nowadays, single production line never satisfies the desire of the modern factories. Especially for those large scaled factories, tool groups consisted of tools with the same functions are often used for mass production. However, the lots must be moved to a proper place for continuously performing the next processes, and furthermore, those tools of tool groups may be allocated everywhere inside the factories. An inferior control method usually moves the lots to an improper place for further processing, and thus seriously influence the process progresses. Therefore, it is important to maintain the tools being operating smoothly.
FIG. 1 represents a factory including six tool groups for performing six specific processes. The first tool group consists of tools 102A, 102B, and 102C for performing the first process. The second process is performed by the second tool group composed of tools 104A, 104B, and 104C. The third process is performed by only a single tool 106A. The fourth tool group consisting of tools 108A and 108B are used to perform the fourth process, and the fifth process is performed by the fifth tool group composed of tools 110A and 110B. The sixth tool group consists of tools 112A, 112B, 112C to perform the sixth process.
Each the above-mentioned tool relates to a specific storage place. For example, the tools 102A and 104C, the tools 102B and 104C, the tools 102C and 104A respectively relate to the storage places 101A, 101B, and 101C. The storage place 103A stores the lots for the tool 106A. The tools 108A and 110B, the tools 108B and 110A respectively utilize the storage places 105A and 105B, and the tools 112A, 112B and 112C also respectively store lots in the storage places 107A, 107B, and 107C.
Please note that any process can export processed lots to any tool of the tool group of the next process. For example, lots exported by the tool 102A can be routed to one of the tools 104A, 104B, 104C. Similarly, those lots processed by the tools 102B and 102C also can be exported to one of the tools 104A, 104B, and 104C. Although the sockets 101A, 101B and 101C are shared sockets, however, one or more transference steps for the lots are required sometime, especially when the selected socket is selected but overloading. For instance, when the socket 101A is overloading, it is better to move the lots to elsewhere. A redundant transference step is thus required to move the lots that will be transferred to the socket 101A. Obviously, the operators have to waste their time to move the lots, and also increase their work burdens.
A simple method for dispatching the lots is to randomly select a tool among a tool group, and to move the lots to the selected socket. Although all the tools of the tool group may work with average loading, the method can not take charge of the entire tool loading. It is clearly not an appropriate control method to be applied in the modern factories. Another control method assigns priorities to tools in each tool group. Every lot is transferred to a storage place of a tool that has highest priority until the storage place achieves full loading, and furthermore, each lot must be sent to the tool with next priority when a tool achieved its full loading.
Suppose that each the first tool of the tool groups in the FIG. 1 has the highest priority, and the loading distributions will be similar to the diagram of the FIG. 2. Obviously, a tool having higher priority will have higher loading at the same time, and those tools having lower priorities are usually idle. Unfortunately, when the factory's productions increase will also increase the differences among the tool loading, which seriously influences the factory's production. A need has been arisen to disclose a method that completely controls the lots dispatch and balances the tool loading for the modem factories.